The invention relates to a tape end alarm for tape recorder.
Many tape recorders are provided with an audible alarm which generates an audio alarm signal when the end of a running tape is detected. Such audible alarms are required when the tape recorder is operating in a record mode. They are not required, however, during a playback mode, since the termination of the audio signal sound being reproduced indicates that the tape has come to an end. For this reason, the production of an audible alarm signal during a playback mode is merely an annoyance. In the prior art tape recorders which include an end of tape alarm, an electrical alarm signal is usually generated by an oscillator which is enabled when an end of tape condition is reached. Particularly, a switch controlling the operation of the oscillator will normally be closed when an end of tape condition is reached and the resulting electrical alarm signal will be applied to an amplifier which energizes a loudspeaker and produces an audible alarm. The audible alarm is normally produced in both the record and playback mode unless a special changeover switch is provided. If a changeover switch is connected in the circuit to prevent the audible alarm from being produced during a playback mode, the provision of the changeover switch causes an increase in the cost of the tape recorder and requires additional space. In addition, since the changeover switch must be completely isolated from the remainder of the recorder circuit, it causes a further increase in the cost.
Another disadvantage of the prior art tape end alarms lies in the fact that during the record mode, the audible alarm is produced while the recording microphone is in its operative condition. As a consequence, when the audible alarm is produced, it is picked up by the microphone amplified by the the amplifier of the recorder, and reproduced by the loudspeaker. As a result of this feedback, sound is produced. Upon occurrence of such howling phenomenon, the audio alarm is very loud and offensive to the ear.